BACKGROUND:
The influence of shoe heel height on venous function is still a controversial
subject in the international literature. The importance of ergonomics for quality
of life is a universally accepted factor, and situations that impair it, such
as prolonged permanence in the supine position, shoe quality and workplace conditions
may interfere with the individual"s health.OBJECTIVE:
To analyze the influence of shoe heel height on lower limb venous drainage using
air plethysmography.METHOD:
Fifteen asymptomatic women with mean age of 24.6 years, wearing shoes of appropriate
size were examined in three different situations: barefoot (0 cm), medium heels
(3.5 cm) and high heels (7 cm). Body mass index was < 25 and the subjects
were classified according to the CEAP International Classification based on
clinical (C0 or C1), etiologic (Ep), anatomic (As) and physiopathological (Pr)
criteria. The values of venous filling index (VFI), ejection fraction (EF) and
residual volume fraction (RVF) were divided into three categories according
to heel height and compared to one another by repeated means analysis of variance
(ANOVA).RESULTS:
EF was decreased and RVF was increased in the high heel group compared to the
barefoot group (p < 0.005). These parameters did not differ between the medium
heel group and the other groups. VFI showed a similar behavior in the three
situations evaluated.CONCLUSION:
High heels reduce muscle pump function, as demonstrated by the fall in EF
and increase in RVF, and their continued use may provoke venous hypertension
in the lower limbs, possibly representing a predictive factor of venous disease
symptoms.

High heels, widely
used among women due to their esthetic value, is no longer exclusive of special
moments and has become a daily option in work environment.

Variations in form,
consistency and material used in shoe manufacturing, especially heel height,
may have an influence on women's health. Volunteers that wore soft shoes after
wearing rigid shoe soles had not only more reported comfort, but also reduction
in edema and in ankle impact after wearing them for only 2 hours.1

Ergonomics and
working conditions, with regard to posture (sitting, standing and walking),
and type of shoes and soil rigidity influence symptoms of tiredness, lumbar
and plantar pain. Such complaints were objectively confirmed based on electromyographic
measurements of the legs and paravertebral lumbar muscles and by means of pressure
and impact sensors installed on shoes.1-3

Air plethysmography
(APG) was used to demonstrate correspondence of complaints of pain and fatigue
in the lower limbs of workers wearing hard shoes and standing upright for a
long time, showing that complaints of fatigue are associated with increased
leg volume.4 Shoe heel thickness and hardness
have orthopedic implications, such as formation of calcaneal exostosis.5
But not everything regarding lower limb health is limited to type of shoe, soil
characteristic or individual's position: walking speed, when increased, raises
plantar pressure peaks,6 and biophysical structure
also interferes with complaints of pain and fatigue, since they are more common
in shorter individuals or in those with more mass.7

Despite the available
knowledge, there is no specific information in the literature about the influence
of high-heeled shoes in venous drainage of the lower limbs.

Thus, this study
aimed at investigating the influence of shoe heel height (3.5 and 7 cm) in venous
drainage of the lower limbs in young women in relation to the bare foot position,
by using APG.

Method

Fifteen asymptomatic
women aged 20-30 years were studied (mean age = 24.6 years). They had body mass
index < 25 and were classified according to CEAP International Classification,
used as a standard in the study of chronic venous disease, in clinical (C0 or
C1), etiologic (Ep), anatomic (As) and physiopathological (Pr) criteria.8

The examinations
were performed at the Laboratory of Noninvasive Vascular Investigation of the
Course of Vascular Surgery at Hospital das Clínicas da Faculdade de Medicina
de Ribeirão Preto da Universidade de São Paulo, Brazil, in the
afternoon and by two examiners. Maneuvers were started after demonstration of
the examination to the volunteer and after gaining her understanding and trust.

APG was performed
in three moments with each volunteer: bare foot (0 cm), medium heels (3.5 cm)
and high heels (7 cm). All the participants were wearing shoes of appropriate
size and signed a consent term approved by the Research Ethics Committee of
Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto
da Universidade de São Paulo, process no. 15.309/2005.

To perform the
examination, the laboratory temperature was maintained between 22 and 24 ºC.
An examination bed was used at a height close to 55 cm to facilitate patient's
mobilization from supine to orthostatic position.

APG consisted of
a device connected by cables to a computer, and a polyurethane hose measuring
2.5 m in length, connected to a 35-cm cuff and approximately 5-L capacity, made
of the same material as the hose.

The examination
was performed with the patient in the supine position for vein emptying, maintaining
her leg elevated at 45º and slightly flexed knee. The patient's foot was
supported by the ankle at a 20-cm height in relation to the examination table.
A pneumatic cuff of an appropriate size was placed in the patient's leg, involving
the whole leg extension, from the knee to the ankle, without exceeding leg limits,
thus allowing a good contact of the cuff with the skin. The latter, in its turn,
caused minimal occlusion of superficial veins.

The device was
then automatically gauged. Cares were taken to prevent the cuff from being in
contact with the support of foot elevation and with the examination table, so
that the reading made by the device and, consequently, the examination result
were not altered.

After an electronic
command, the cuff was automatically inflated until selected pressure of 6 mmHg,
and the data were transmitted to the pressure transducer, located in the device,
amplifying the signal and registering it as a graph in the computer screen.

A basal volume
value was obtained and then the patient was requested to raise her leg aided
by the examiner, standing on the unassessed limb. The patient placed her hands
on a walking device for better balance. Increased leg volume was observed until
reaching a plateau, indicating that the veins were full. The difference between
initial and plateau volume represents functional venous volume (VV).

Next, the patient
was requested to stand on both feet and perform a plantar flexion movement,
causing calf muscle contracture, resuming then initial rest position or relaxation
of assessed limb. Decrease observed in the graph curve corresponds to ejected
volume (EV), resulting from calf muscle contraction.

After this movement,
a new plateau is reached (usually more elevated than the initial plateau) and
the patient was requested to perform 10 movements of plantar flexion in a velocity
of one movement per second. Decreased volume was also recorded. Residual volume
(RV) was calculated based on final basal value in relation to remaining volume
at the end of movements.

After plantar flexions
were over, the patient was requested to resume rest position and relax assessed
limb until reaching a new venous filling plateau. After leveling, with the aid
of the examiner, the patient returned to supine position on the examination
table with the foot on the support, and total limb emptying was recorded, shown
by a graph leveling corresponding to final volume (FV).

After markings
were placed in the graph, the computer automatically processed the calculations
for venous filling index (VFI), ejection fraction (EF) and residual volume fraction
(RVF).9

After the procedure
described above was finished with the volunteer bare foot, the same routine
was repeated with the volunteer wearing shoes in both feet, first with a 3.5-cm
heel and then with a 7-cm heel, resulting in three graphs per volunteer. The
cuff was always placed in the left leg.

VFI is the variation
of volume produced in the limb divided by the corresponding time in seconds,
when passing from the supine to the orthostatic position, calculated using the
formula VFI = 90% x VV / VFT 90 and expressed in mL/s.

We studied the
calf pump function using the data obtained from the variables EF and RVF.

EF provides an
estimate of venous reflux during physical activity and the changes that result
in less ejected blood. EF is the percentage of total venous volume, ejected
in a single calf muscle contraction. It is calculated by the formula EF = (EV
/ VV) x 100, where EV is ejected volume and VV is venous volume.

To compare the
values of variables VFI, EF and RVF between plain, medium and high heels, variance
analysis was used for repeated measurements (ANOVA), considering significance
level of p < 0.05 by Bonferroni post hoc test.12

Results

VFI, EF and RVF
values were divided into three categories according to heel height: bare foot
(0 cm), medium heels (3.5 cm) and high heels (7 cm). To facilitate reading and
understanding of results, those values are presented in tables and figures.
There was reduction in venous drainage demonstrated by EF reduction (Figure
2 and Table 1) and increase in RVF (Figure
3 and Table 2) for the high-heel group (7 cm) compared
with the bare foot group (0 cm).

There was no significance
difference in these parameters between the medium-heel group and the other groups,
although there has been a strong tendency in reduced EF and increased RVF in
this group compared with the bare foot group.

APG is a method
of great value in assessing the venous system of the lower limbs, allowing clinical
and physiological correlations.13 APG quantifies
venous volume, superficial and deep venous reflux in mL/s, degree of venous
obstruction and ejection capacity of calf muscle pump noninvasively, according
to blood flow graphs obtained during the maneuvers.14
According to Yang, in addition to that information, APG can reveal elements
that help therapeutic management and assess the effect of the proposed treatment,15
including by characterizing hemodynamic study during use of elastic compression.16

Assessment of calf
muscle pump function according to age17 and the
effects of calf muscle strengthening in venous hemodynamics18
have been observed using APG.

RVF expresses the
combined effect of venous reflux and ejection fraction with rhythmic exercise.
In addition, since it is a relevant indicator of outpatient venous pressure,
it was one of the parameters chosen to assess the influence of different shoe
heels in venous hemodynamics.19

The main mechanism
of venous reflux in the lower limbs is blood ejection through muscle contraction.
The "calf pump" is activated at each step, ejecting blood against gravity and,
due to venous valve competence, there is no reflux.

Ankle mobility
is an essential factor for an efficient performance of the calf pump. When tibial-tarsal
ankylosis is installed, there is irreversible chronic venous insufficiency,
because the gemellus-soleus pump function is cancelled.20
Calf contraction during walking aims at elevating the body on tip toes, impelling
it. Apparently, high heels limit this movement radically, reducing pump action.
The higher the heels, the higher the intensity of this phenomenon.

The degree of ankle
mobility in a normal individual is around 70º, 45º due to plantar
flexion and 25º due to dorsal extension. After studying 32 limbs of 26
male adults, Back et al.21 concluded that a limited
degree of ankle mobility is a significant factor in venous ulcer index. Use
of high heels is clearly not a definite change, but considering "exposure time,"
different impairment levels could occur.

In this study,
there was no difference in VFI in the three moments (bare foot, 3.5-cm heels
and 7-cm heels, respectively) tested, which shows that global valve competence
of the venous system of lower limbs was preserved during the three stages of
the experiment, a result that confirm the selection criteria of not having venous
disease of any type in assessed women.

EF was reduced
when volunteers were wearing high heels, which can be explained by a lower shortening
of calf muscle fibers during muscle systole. Consequently, blood volume retained
in the limb increases.

Increased RVF when
wearing high heels (7 cm) found in this study is mainly due to higher blood
residue that remains in the limb after EF fall, considering that RVF is obtained
in muscle diastole and represents the sum of residual venous volume and arterial
blood supply coming to the calf.

Despite the impossibility
of confirming a significant difference between the medium-heel group (3.5 cm)
and the other groups, there is a strong tendency to EF reduction and RVF increase
in this group compared with the bare foot group. In further studies, using a
larger population, such tendency is likely to be corroborated with statistical
significance.

We conclude that
high heels reduced calf muscle pump function and that its continuous use can
cause a status of venous hypertension in lower limbs. That situation is an essential
component in venous disease evolution from lower to higher clinical severity
states.

This study was
carried out at the Course of Vascular Surgery and Angiology, Department of Surgery
and Anatomy, Faculdade de Medicina de Ribeirão Preto, Universidade de
São Paulo (USP), Ribeirão Preto, SP, Brazil. It was presented
and received a second place award at the IX Panamerican Congress on Vascular
and Endovascular Surgery, held in Rio de Janeiro, Brazil, from October 31 to
November 4, 2006.